Lighting 1.pdf

Electrical Installation

Lecture No.11

Dr.Mohammed Tawfeeq Alzuhairi

Lighting design and calculations THE LUMEN METHOD This method is also called: Photometrical Computation and mostly used for interior lighting calculation To determine the total number of luminaires required to produce a given illuminance by the lumen method we apply the following formula: Total number of luminaires (N) required to provide a chosen level of illumination (E) at a given surface is .

where  E = the illuminance level is chosen after consideration of the IES code, the area is the working area to be illuminated, the lumen output of each luminaire is that given in the manufacturer’s specification and may be found by reference tables.  MF is maintenance or (the light loss LLF) factor. This factor depends on the maintenance staff of the building, but in general it is taken as 0.8 -0.9.  Utilization factor (UF) The light flux reaching the working plane is always less than the lumen output of the lamp since some of the light is absorbed by the various surface textures. The method of calculating the utilization factor (UF) is detailed in lighting design books, although lighting manufacturers’ catalogues give factors for standard conditions. The UF is expressed as a number which is always less than unity; a typical value might be 0.9 for a modern office building. 1